A noncontact surface shape measuring apparatus of laser probe type using laser autofocusing is used to measure the shape and roughness of a precision component. The top face of a work which is a measurement object is scanned in a horizontal direction at predetermined pitches with a laser beam under autofocusing control. According to a movement amount of an objective lens of an autofocusing optical system in a focusing direction, measurement data related to a surface shape of the work is obtained.
The objective lens is controlled so that, as disclosed in Japanese Patent No. 2125498, a return beam of a laser probe is received at the center of a two-piece sensor. Namely, the work is fed at predetermined pitches, and when a movement of the objective lens causes a return beam from the work to hit the center of the two-piece sensor, it is determined that a focused state is established. Then, an amount of the movement of the objective lens is detected to get height information of the surface of the work. The height information about the surface of the work is obtained at the predetermined pitches, to measure a surface shape of the work.